1. Field of the Invention
This invention relates to electromechanical relays for switching high-frequency signals with high reliability, stable insertion loss, stable return loss and high isolation.
2. Description of the Prior Art
Many different types of switches are known for the switching of radio frequency signals and other signals. Some switch types include spring actuated contacts, electromagnetic actuators, plungers with permanent magnets, articulated joints and other movable elements. Examples of these types of switches are shown in U.S. Pat. Nos. 6,340,923; 6,337,612; 6,204,740; 6,124,771; 5,894,255; 5,815,049; 5,724,014; 5,699,030; 5,652,558; and, 5,499,006. The switches using conductive reeds or similar elements generally use a conductive element made from beryllium copper which is plated with a high conductivity material. Unfortunately these switch types suffer from poor reliability and low switch lifetime. Plating variations contribute to variations in contact resistance, which in turn affect the life of the switch. Additionally, the life of a switch depends on how quickly the electrical contact surfaces develop a layer of contamination. By making the reed of thinner and more flexible material than is generally found with plated beryllium copper, a so-called “wiping action” is able to take place that will remove contaminants during each switching cycle.
Other examples of radio frequency (RF) switches are shown in U.S. Pat. Nos. 6,133,812; 6,037,849; 4,908,588; 4,697,056; and, 4,298,847. The RF switches shown in these patents use several cylindrical guide pins to guide the reed conductors in an up and down motion preventing contact between the reed conductors and the walls of the surrounding RF channels.
Guide pin wear is a significant component in the loss of reliability of RF switches and thus in potential early failure. One method of reducing wear in the guide pins is to increase the contact area between the guide pins and the reed conductors. This method is illustrated in U.S. Pat. Nos. 5,815,057 and 5,642,086.
A further improvement to RF switches is offered by U.S. Pat. No. 6,650,210, in which U-shaped guide members increase the lifetime of the RF switch by reducing stresses in the contact area between the reed conductors and the guide pins. However, the form of the prior art 2-part enclosure leads to some performance problems. The U-shaped guide members require extremely precise locating in the switch, otherwise wear becomes excessive and failure-inducing wear particles are generated. Also, the case has concentric holes into which actuators are installed and reed holders are located. The reed holders move within these holes to bring the reeds between contacting and non-contacting positions. Because of the structure of the case, the holes are partially blind and cannot be machined with very high precision. Additionally, the outside of the case wall forms part of the RF cavity for the switch and also serves as ground. Thus, the wall and therefore the whole case requires plating with high conductivity material. As the plating adds dimensional variations, problems with electrical performance may result. A further problem with prior art switches occurs when, during operation, a portion of the reed holder rubs against the inside of the RF cavity creates additional wear particles. Even with the improvements in the prior art devices which may offer a lifespan of up to 2 million cycles, a need remains for an RF switch that has a longer lifespan and higher reliability with precision operation. Rather than using the traditional 2-part case of the prior art, a more reliable switch may be made with a 3-part case which eliminates the need for machining blind holes and performing unnecessary plating.